1. Field of the Invention
The present invention relates generally to evaporative emission control systems for automotive vehicles and, more particularly, to a leak detection assembly and method for determining if a fuel cap sealing problem is present in an evaporative emission control system for an automotive vehicle.
2. Description of the Related Art
Modern automotive vehicles typically include a fuel tank and an evaporative emission control system that collects volatile fuel vapors generated in the fuel tank. The evaporative emission control system includes a vapor collection canister, usually containing an activated charcoal mixture, to collect and store volatile fuel vapors. Normally, the canister collects volatile fuel vapors which accumulate during refueling of the automotive vehicle or from increases in fuel temperature. The evaporative emission control system also includes a purge valve placed between an intake manifold of an engine of the automotive vehicle and the canister. The purge valve is opened by an engine control unit an amount determined by the engine control unit to purge the canister, i.e., the collected volatile fuel vapors are drawn into the intake manifold from the canister for ultimate combustion within a combustion chamber of the engine.
Recently, governmental regulations have required that certain automotive vehicles powered by volatile fuels such as gasoline have their evaporative emission control systems checked to determine if a leak exists in the system. As a result, on board vehicle diagnostic systems have been developed to determine if a leak is present in a portion of the evaporative emission control system. One such diagnostic system utilizes a vacuum regulator/sensor unit to draw a vacuum on the evaporative emission control system and sense whether a loss of vacuum occurs within a specified period of time.
Diagnostic systems also exist for determining the presence of a leak in an evaporative emission control system which utilizes positive pressurization rather than negative pressurization, i.e., vacuum. In positive pressurization systems, the evaporative emission control system is pressurized to a set pressure, typically through the use of an electric air pump. A sensor determines whether the pressure remains constant over a certain amount of time.
At times, a leak will exist in the system due to a fuel cap sealing problem. That is, the fuel cap is either missing, loose, or is not properly sized to the fuel tank fill tube. Present diagnostic systems do not specifically perform a test to identify this type of leak condition. As such, the sealing problem is not detected until operation of the standard diagnostic test. Further, conventional diagnostic systems treat such a leak condition the same as other types of leaks thereby activating the warning signals and/or setting fault codes. Such warning signals and fault codes are typically not cleared until after three cold starts, i.e., three days. As such, vehicle operators are taking their vehicles to dealerships for repair when a simple check and resealing of the fuel cap may resolve the situation.
In view of the foregoing, it would be desirable to provide a leak detection system for specifically determining if a fuel cap sealing problem is present in the evaporative emission control system of the automotive vehicle and informing the operator or service technician of the same.